The invention relates to transparent polyamide moulding materials. More specifically, the present invention relates to polyamide moulding materials having an optimum transparency and optimum chemical resistance as well as high permanent fatigue strength.
Two polymer types are known in the field of transparent polyamides having a high light transmission, high permanent fatigue strength and excellent chemical resistance.
Microcrystalline, transparent polyamide moulding materials having excellent chemical resistance, especially to alcohols, which are produced from PACM having 35-60 mole-% of the bis-(4-aminocyclohexyl)methane trans,trans-isomer, 65-40 mole-% of other diamines and dodecanedioic acid are known by DE 43 10 970. A disadvantage is the low glass transition temperature (Tg) being 140° C. and the low stiffness. Due to the microcrystalline phases, the transparency does not achieve the optimum. The permanent fatigue strength for these polyamide types for defined initial bending stresses shows low numbers of cycles to break in fatigue test after Wöhler.
Amorphous, transparent polyamide moulding materials which have high chemical and thermal resistances and an excellent permanent fatigue strength to fatigue test after Wöhler and which are constituted from MACM (bis-(4-amino-3-methyl-cyclohexyl)-methane) and dodecanedioic acid are known by EP-A-0 725 101. With regard to the microcrystalline, transparent polyamides, the resistance to alcohols is lower. The transparency is comparable to the PACM12 types, but is not yet optimum.
DE 196 42 885 C2 describes amorphous, transparent polyamide moulding materials containing at least a second homopolyamide which show an excellent permanent fatigue strength besides the properties described in EP-A-0 725 101 and which are suitable for producing moulded parts for electro-optical applications such as lenses for sunglasses and opticals waveguides.
At mechanical loading of the surfaces, transparent polyamides have a high abrasion resistance and a good scratch resistance which can be further improved by a coating with hard lacquer.
Transparent polyamides are advanced polymers which are used especially in the field of aggressive media and in the field of high pressure load and high permanent fatigue strength. Simultaneously, transparent polyamides have high glass transition temperatures (Tg) and achieve high thermal resistance.
For example, aggressive media at high temperatures are present in dish-washers or media-conducting systems to which transparent mass-produced materials such as PS (polystyrene), PMMA (poly(methyl methacrylate)), PET (polyethylene terephthalate), PVC (poly(vinyl chloride)) or PC (polycarbonate) do not resist. Application examples are baby bottles, bottles for carbonating, dinner-service and cutlery handles. For example, resistance to chemicals in connection with thermal resistance and permanent fatigue strength are required for viewing glasses in the field of heating techniques and service stations having direct fuel or oil contact, filter cups for drinking water treatment and media filtration, flowmeter for gases or liquid media, lamp cases, reflectors for auto lamps and sensors. The importance of transparent polyamides for external use increases because high weathering resistances are achieved by a combination of cycloaliphatic diamines having long-chain aliphatic dicarboxylic acids, which can be adjusted optimally by the tertiary butylphenol class and HALS types stabilizers.
Further, lacquering processes require chemical resistance to avoid stress cracks to the solvents, but require simultaneously an activability of the surfaces to achieve an optimum lacquer adhesion. Numerous lacquers such as hard lacquers for increasing the scratch resistance require hardening temperatures up to 130° C.
High permanent fatigue strength in combination with a very good thermal and chemical resistance are required also in the field of spectacles and safety spectacles besides the engine construction and the medicinal techniques.
Spectacle glasses for sunglasses and correction spectacles can be produced due to the favorable optical properties such as refractive index and Abbe coefficient and transparency. Also, lenses for technical devices, lights or signal lamps, opto-electronic couplers or LEDs can be produced. These applications require the optical properties as well as an improved transparency and clarity as well as simultaneously a high temperature stability with a very low discoloration of the materials. The combination of suitable properties for spectacle frames and spectacle lenses of amorphous polyamides having an excellent resistance to chemicals and stress cracks allows new design forms for spectacles having bores for positioning screws directly in the spectacle glass, which leads to cracks and breaks for traditionally used materials such as glass, PC or PMMA.